690 T. C. CHAMBERLIN 



Case II. The questionable intimations of the craters of the moon.— 

 The impact theory of the craters of the moon affords a concrete 

 basis for the study of infalls of a still larger order. To fit this case, 

 bodies of the order of five miles in diameter, more or less, seem to be 

 required, and for working convenience these may be given the 

 specific gravity of the moon, 3 .34. The assumed size in this case 

 has about the same ratio to the larger order of the moon's craters 

 that the assumed 400 or 500 foot meteoritic body had to the size 

 of Meteor Crater, but the mass is made relatively less to be in 

 better accord with the moon's mass. The size is about the lower 

 limit assigned to planetoids. No atmosphere can be supposed to 

 have broken the effects of infall in this case or to have checked 

 the free dispersal of the debris. 



In the previous case there was surprisingly little evidence of 

 liquefaction. What is the evidence here ? The steep walls of the 

 deep craters are quite incompatible with a liquid state, so far as 

 this outermost part is concerned and this is the part subject to 

 direct impact. There was strength enough in the crust to support 

 the lunar Alps and Apennines, some of whose peaks tower to 

 heights of 20,000 feet and more above the adjacent surface, i.e., 

 5,000 feet higher than their terrestrial prototypes. No less than 

 ten mountain ranges have been recognized on the moon, which 

 implies general crustal strength. The great relief of such eleva- 

 tions towering above such depressions is uncontrovertible evidence 

 of strength and stability. The significance of this is emphasized, 

 if the supposed impacts are made a part of the formative process 

 of the moon, for then they are very old and have stood in this 

 strong relief in spite of all the creep of the geologic ages. 



A search for direct evidences of molten matter gives meager 

 results under the most favorable interpretation that is tenable. 

 Such of the craters as have level bottoms have been thought to 

 imply a partial filling of lava, supposed to have risen from below 

 after the craters had been formed. These bottoms may, however, 

 be interpreted as level beds of clastic debris, like those that form 

 the level bottom of Meteor Crater. So, also, the seemingly smooth, 

 but really quite accidented, plains of the "maria" have been inter- 

 preted as great lava flows, but these may likewise be merely debris 



